There has never been any doubt about the Crawleys' wealth. The trappings surround the family—who we greeted on screen tonight in Downton Abbey's third-season premiere—and, at times, threaten to consume them.

The Crawleys support a small fleet of servants, as well as a village. Dinners are enjoyed in white tie and tail-coats. Weddings assume fairy tale-like proportions.

The centerpiece: Downton Abbey, the ancestral estate, a splendid mansion in Southern England replete with everything you'd expect—17th century Dutch masterpieces hang in the orange-hued smoking room. Down the hall, floral wall panels adorn the library, brought to Downton from Spain by the third earl.

Just the sort of place in which you can truly relax on the weekend.

Now, though, all this wealth is in doubt. The Crawleys have proven to be pound-foolish once again. As the new season begins, Robert Crawley, the current Earl of Grantham and family patriarch, has apparently committed several basic investing mistakes. First, he placed too great a sum in a single stock, a Canadian railroad company. The company went bankrupt, lost its chief executive and will soon be absorbed by the government. Result: a complete loss of principal.

"Investing in one enterprise, wasn't that foolish?" his wife, Cora, asks him. Indeed. Diversification is key to any sensible allocation strategy.

Lord Grantham had relied too much on other people's forecasts. He, in fact, violated a key rule that Benjamin Graham would espouse a decade later in The Intelligent Investor: any investment must be made on fundamental research that you conduct yourself. Moreover, the earl erred by trying to catch a large macroeconomic headwind—that a post-war boom would boost the railroads—instead of investigating whether the particular company could take advantage of such a tailwind. (Today, that would be akin to investing in homebuilders, such as Toll Brothers or K.B. Homes, instead of opting for something safer and less cyclical, like a Coca-Cola or a Wal-Mart.)

These investing blunders, of course, were not the first time that the Crawleys have proved to be a family possessed of considerable wealth, but little financial wisdom. Lord Grantham's father made a serious estate planning mistake. The deceased pater familias created an entail that allowed the family inheritance to pass only to a male heir. It was virtually unbreakable; to do so would have required a bill from Parliament. Unfortunately, the earl had no grandsons, meaning the fortune would go to a complete stranger. Worse still, most of that inheritance came not from the Crawleys, but Robert's wife, an American heiress.

Certainly, amassing a fortune—$1.1 billion by our estimates—requires some cunning. So, there's every possibility that the Crawley coffers can be refilled. Else, they may find themselves missing from next year's Fictional 15, FORBES' annual estimates of fiction's wealthiest characters. Such a slight would probably betray our American sentiment and plainspoken manner, but we have realized that Lord Grantham himself is not above a guest-list snubbing to make a point.

To be sure, eldest daughter Mary, who has now wed that distantly related heir, seems dead set on raising her brood in Downton. She's proving to be something of a English pastoral Scarlet O'Hara. She'll now have her work cut out for her—remember what we said about the family's tony mentality being a curse sometimes?

The Crawleys can take some solace, though. In 1920, a key bit of reading material for the well-heeled had recently arrived on the scene: FORBES magazine had appeared on newstands at that point for a little more than three years.